1. Field of the Invention
The present invention relates to a shock absorptive support structure adapted for elastically supporting a top plate on support brackets in a coupler commonly referred to as a fifth wheel for coupling a tractor and a trailer.
2. Description of the Related Art
As a tractor coupled to a trailer is driven to travel in a direction, a relative displacement in the coupler inevitably occurs between the support bracket and the top plate in a direction corresponding substantially to the direction of travel and in a vertical direction. To solve this problem, the elastic support structure conventionally has been adopted so that the relative displacement between the support bracket and the top plate can be alleviated. For example, according to the disclosure of Japanese Utility Model Application Disclosure Gazette No. 1985-195205, the bottom of the top plate is provided with a downward extending projection to surround a space destined to receive a first elastic member having a concave bottom, while the upper end of the support bracket is provided with a boss having a convex top and a transverse through-hole. The boss is inserted tightly into the concave bottom of the first elastic member so that the top plate may be elastically supported on the support bracket. A support pin is inserted into the through-hole of the boss to fix it across the space defined by the projection extending downward from the bottom of the top plate and then a second elastic member is disposed between this support pin and the top of the boss.
The above-mentioned well known shock absorptive support structure satisfactorily functions in practice to assure safety as well as driving comfort as long as the support structure is relatively new. However, the same shock absorptive support structure is disadvantageous in that the elastic member is worn away after the coupler has been used for a relatively short period. Consequently, undesirable inter-metal contact or collision occurs between the top plate and the support bracket, generating abnormal noise as the tractor coupled to the trailer is driven. Shock caused by such inter-metal contact or collision is transmitted to the driver's seat and not only affects driving comfort but also causes breakage of parts of the support bracket, such as the boss, and eventually affects driving safety.